Effect of Sub-inhibitory Amounts of Nisin and Mineral Salts on Nisin Production by Lactococcus lactis UQ2 in Skim Milk

Abstract

The effect of nisin regulatory system of the quorum-sensing mechanism and mineral salts on the production of nisin A by the native strain Lactococcus lactis UQ2 growing in skim milk was evaluated using a static culture. A 6 × 3 full factorial design with two replicates was conducted, aiming to study nisin production during growth of L. lactis UQ2 in skim milk as model food. At appropriate time intervals, the produced nisin, microbial population, and medium pH were measured. Sub-inhibitory amounts of commercial nisin (IN; 0, 0.05, 0.65, 1.25, 1.87, and 2.5 μg/L) were added as inducer to skim milk. A mixture of Mg/Mn (MS; 0, 0.5/0.1, and 0.2/0.04 g/L) was also added. These two factors (IN, MS) and their interactions were highly significant for nisin production by L. lactis UQ2. The highest nisin production (75 ± 7 IU/mL) was achieved at 10 h of incubation, for treatment containing 1.87 μg/L of IN and MS 0.5/0.1 g/L, while only 3.5 ± 0.5 IU/mL were produced by control cultures at 6 h. In contrast with other reports, nisin production started at mid-log phase, and the maximum activity was observed well beyond the beginning of the stationary phase (6 h). This was attributed to the effect of IN. Semi-quantification of thhttps://digital.csic.es/listadoMetadatos.jsp?ID=autores&vocabulary=autores&plataforma=pasarelae structural nisin gene nisA by reverse transcriptase-polymerase chain reaction indicated that it was expressed 2.2 times more than the control treatment. L. lactis UQ2 is different from most strains of this genus, because of its poor lactose consumption and lactic acid production when growing in skim milk. Given the capacity of nisin production and the well-known antimicrobial properties of this bacteriocin, this strain may be useful to enhance the safety of low acidity dairy products such as Mexican-style fresh cheese. © 2009 Springer Science + Business Media, LLC.Peer Reviewe